Rust Interview Questions & Tips

By Aline Lerner | Last updated: July 12, 2023

Rust Interview Stats

We've hosted over 100k interviews on our platform. Rust was the language of choice in those interviews 0.2% of the time. Rust also had the highest success rates – engineers who chose Rust as their interview language passed their interviews 82% of the time.

Below is a distribution of programming languages and their popularity in technical interviews as well as success rates in interviews, by language.

Rust Idioms & Idiosyncrasies

As a modern and advanced language, Rust has a lot of complexity and a lot of still-evolving features. It’s an opinionated language that was designed and continues to be built by people who are morally opposed to hand waving. It’s a language and culture with a fair amount of computer science formality, especially with respect to the type systems.

Candidates and interviewers may be more or less familiar with Rust’s type systems and other internals. The most important recommendation we can make is to make sure that if you’re using Rust-specific terms to describe what you’re doing that you truly understand what they mean. It’s not expected that you’ll know all the details for an interview – and an understanding of all formal definitions is required – but you should be careful not to overreach, and you definitely shouldn’t try to hand wave your way through any explanations, as you’ll find that the tolerance for hand waving among Rust interviewers is much lower than in other interview contexts.

With that in mind, here are some key, idiomatic concepts you’ll want to be very comfortable with:

• Ownership, borrowing, and lifetimes. Rust's ownership model is central to the language and distinguishes it from other systems languages. Make sure you understand concepts like ownership, borrowing, lifetimes, and how they prevent data races and memory leaks.
• Pattern matching. Rust provides powerful pattern matching capabilities through the match keyword. Be familiar with pattern matching syntax and its various applications, such as destructuring enums and matching on values.
• Error handling. Rust emphasizes explicit error handling to prevent unchecked errors. Know the difference between Result and Option types and how to use Result's unwrap, expect, and match methods. Be aware of error propagation techniques, like the ? operator.
• Collections and iterators. Rust provides a rich set of collection types and powerful iterator functionality. Be comfortable working with vectors, hash maps, and other collections, as well as using iterators to perform transformations, filters, and aggregations.
• Traits and generics. Traits allow for code reuse and polymorphism in Rust. Understand how to define traits, implement them for custom types, and use generic functions and structs to write flexible and reusable code.
• Unsafe Rust. While idiomatic Rust encourages safe programming, understanding unsafe Rust is crucial for dealing with low-level operations or interacting with external code. Know how to use unsafe blocks and functions responsibly, ensuring memory safety and avoiding undefined behavior.
• Cargo and the Standard Library. Familiarize yourself with Cargo, Rust's build system and package manager. Understand how to create, manage, and publish projects using Cargo, as well as how to leverage the standard library's modules and functionality effectively.

Common Rust Interview Mistakes

First and foremost, as with any language, you should NOT choose Rust as a way to show off if you don’t know it well. Make sure that you pick a language you are very comfortable with, have used at work recently, and have interviewed before.

Outside of that, here are some things you should try to avoid when interviewing in Rust specifically.

• Using a bunch of unsafe blocks. Sometimes that may be handy for temporarily working around a compilation problem or quickly accomplishing a task during an interview, but in general the people interviewing you in Rust are going to want to see you use the language's safety features.
• Not doing proper error handling. In most cases, the compiler will stop you from not handling an unexpected value/result, but having default panics on almost every line is not idiomatic Rust. In other words, don’t do this:

use std::fs::File;
use std::io::Read;

fn read_file_contents(file_path: &str) -> String {
    let mut file = File::open(file_path).unwrap();
    let mut contents = String::new();
    file.read_to_string(&mut contents).unwrap();
    contents
}

fn main() {
    let file_path = "nonexistent_file.txt";
    let contents = read_file_contents(file_path);
    println!("File contents: {}", contents);
}

• Make sure you understand the core principles (e.g., memory allocation, memory safety) and the motivations for why the language is designed the way it is, rather than focusing on the latest Rust nightly feature. This is a common failure mode for people who are coming from higher-level languages.
• Understand the borrow checker. If you don’t know what the borrow checker is and what kind of problems it’s trying to prevent, you’re going to have trouble building rapport with some Rust interviewers.
• Use crates that you’re familiar with, even if your interviewer suggests a specific one. For some interview questions, you may find that using a particular crate will make things a lot easier, and that’s fine as long as you’re familiar with it. You might run into a situation, however, where your interviewer proposes that you use a crate that you aren’t familiar with. For example, there are different crates for ORMs, async.io frameworks, and web frameworks – multiple ways of doing the same thing– so it’s entirely possible that you’re more familiar with one and your interviewer is more familiar with another. It’s better to demonstrate mastery over something that you know well rather than coding on your back foot.

How to Demonstrate Rust Expertise in Interviews

To impress your interviewer, go deep on some of the core ideas behind the Rust type system and the core ideas on the borrow checker and the way it does Rust memory management and why.

More senior engineers who are already working in Rust daily and are involved in the community can demonstrate knowledge of the latest Rust language proposals and advanced nightly features. Keep in mind, however, that this demonstration of mastery is only credible if it takes place on top of a strong foundation of fundamentals that you’ve already established earlier in the interview. Otherwise you might come off like you’re hand waving… which we sternly talked about in the beginning.

Rust Interview Replays

Below you can find replays of mock interviews conducted on our platform in Rust. The questions asked in these interviews tend to be language-agnostic (rather than asking about language-specific details and idiosyncrasies), but in these cases, the interviewee chose Rust as the language they would work in.

\ \ Amazon Interviewer \ Meeting Rooms \ Rocket Samurai, an Amazon engineer, interviewed Professor Squirrel in Rust](/content/mocks/amazon-rust-minimum-room-count/index.html)

\ \ Google Interviewer \ K nearest restaurants \ Immutable Automaton, a Google engineer, interviewed Professor Squirrel in Rust](/content/mocks/google-rust-k-nearest-restaurants/index.html)

\ \ Google Interviewer \ Design a leaderboard \ Red Maelstrom, a Google engineer, interviewed Professor Squirrel in Rust](/content/mocks/google-rust-design-a-leaderboard/index.html)

\ \ Google Interviewer \ Rate Limiter \ Doctor Squab, a Google engineer, interviewed Professor Squirrel in Rust](/content/mocks/google-rust-rate-limiter/index.html)

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